Lewis Holtby's former youth coach Max Eberl says he worries that the 22 year old doesn't have the physical attributes to compete in the Premier League, with the midfielder set to be tested when he makes a move to Tottenham in the summer.
Spurs beat off competition from Arsenal and Liverpool to sign Holtby, with the star coming to the final six months of his contract with Schalke and looking for a move to the Premier League.
And Erbel, who was sporting director at Borussia Monchengladbach when Holtby was a youngster at the club, says that while he has a lot of skills to offer Tottenham, he will need to work on the physical side if he hopes to impress in England.
"Lewis Holtby is from our youth academy," he said, according to Goal.com. "We educated him since [he was] 15 years old then he went to Alemannia Aachen and the rest of the career is known. And now he decided to go to Tottenham.
"I think it's a big step for him. I hope he will play for Tottenham because it's a very good team. The Premier League, it's a very competitive league.
"So he decided to go this way and everybody will wait and see what happens. But he has technical quality, he has the football quality. But I think he needs physical quality too, in England, in the Premier League, and that will be the little question mark [over his ability]."
Holtby was another fine piece of business for the north London club, who were also able to wrap up a deal for long-term target Ezekiel Fryers in the opening week of the January transfer window.
Many have talked up the Germany international's ability, and he admitted that if Tottenham hadn't come in with an offer, he would have stayed at Schalke beyond the summer.